I am looking around for a specific indicator for ferric ions that's very specific for ferric over ferrous. It should be water soluble and stable at room temperature and neutral or basic pH. In addition, it should be very sensitive and should be able to detect slight increases in ferric concentration by a bright colour change. And of course, the colour change should be easily detectable by a spectrophotometer, or more preferably, by the human eye.
Help will be much appreciated!
The Rhipidothyrididae: Brachiopods of the Devonian
23 hours ago in Catalogue of Organisms